Plasmodium yoelii: effects of red blood cell modification and antibodies on the binding characteristics of the 235-kDa rhoptry protein.

The 235-kDa rhoptry protein of the rodent malaria parasite Plasmodium yoelii yoelii was shown to bind to the surface of mouse red blood cells in a calcium-independent process, using a erythrocyte-binding assay. This binding is affected by modification of the surface of the red blood cells by enzymatic treatment. Chymotrypsin and trypsin but not neuraminidase treatment of the erythrocytes significantly reduced the binding of the 235-kDa proteins. The binding of an unrelated 135-kDa protein was abolished by treatment with chymotrypsin. Although the 235-kDa proteins bind to both reticulocytes and mature red blood cells, the binding to mature cells was more pronounced. In the presence of hyperimmune infection serum or specific polyclonal antibodies to the 235-kDa protein its binding to erythrocytes was reduced, further demonstrating the specificity of this ligand-receptor interaction.